The goal of this project is to develop a test kit to replace the 72-h stool fat test in the clinical management of patients with cystic fibrosis (CF). We propose that this can be accomplished by feeding a test meal containing both 1,3-distearyl, 2[13C]octanoyl glycerol (S-*O-S) and the nonabsorbable marker dysprosium chloride (DyCl3) followed by analysis of a single stool. This new approach will be: 1) highly correlated with 72-h stool fat, 2) significantly less tedious to perform, and 3) highly reproducible. Phase I studies have shown that Dy is quantitatively excreted by CF patients and follows the same excretion kinetics as 13C- labeled triglyceride (TG), thus, the feasibility has been demonstrated. During Phase II we will study details of the approach in order to develop a practical test kit for wide-spread use to include: 1- Demonstrating that absorption of S-*O-S is reproducible. 2- Demonstrating that absorption of S-*O-S accurately reflects the degree of malabsorption observed in individual CF patients. 3- Validating use of a single stool for quantifying labeled fat excretion. 4- Refining analytical procedures that would lower the cost of the resultant test kit. Once the test kit and procedure are developed it will be marketed through BioChemAnalysis Corporation together with the required analytical services (Phase III) to the biomedical community at large. PROPOSED COMMERCIAL APPLICATION: This research will lead to the availability of a test kit and procedure for the accurate measurement of fat absorption that is non-invasive and requires the collection of only a single stool. Because the procedure will be highly reproducible and accurate as well as relatively simple to use it will be applicable to routine clinical use in the management of individual CF patients as well as to use in research protocols.